In a general turbine (for example, steam turbine), a rotor that is a rotational shaft is rotatably supported at a casing, turbine blades are installed at an outer peripheral portion of this rotor, also turbine vanes are installed at an inner wall of the casing, and the multiple turbine blades and turbine vanes are alternately arranged on a steam passage. Furthermore, the turbine blades and the rotor are rotationally driven in a process in which steam flows in the steam passage.
The turbine blade includes a blade root portion fixed to a rotor disk of the rotor, a platform integrally formed with the blade root portion, and a blade portion having a base end portion joined to the platform and extending to a tip end portion side. Additionally, a plurality of turbine blades is fixed at their base ends to an outer peripheral portion of the rotor disk so as to be arranged in a row in a circumferential direction thereof.
For example, turbine blades of a steam turbine are rotated inside a route where steam flows. At this point, the steam near a final stage of a low-pressure steam turbine includes a large amount of small water droplets. Therefore, a front edge portion of a blade tip end is thinned due to erosion caused by high-speed collision of the water droplets.
As a countermeasure against such erosion, there is a method of forming an erosion shield at the front edge portion of the tip end of the turbine blade as disclosed in Japanese Laid-open Patent Publication No. 10-280907 and Japanese Laid-open Patent Publication No. 2012-86241, for example. In Patent Literature 1, an erosion shield is formed by applying cladding by plasma transfer arc welding. Furthermore, Patent Literature 2 discloses a technology in which hard material powder is molten by high-density energy irradiation (laser and electron beam) to form a hard layer by cladding by welding, and an erosion preventing portion (erosion shield) is provided by locally replacing a part of a member with the hard layer.